To provide an automatic excretion disposal apparatus and a user-worn device which enable a sufficient excretion and washing and are user-friendly.

The user-worn device comprises a diaper cup 10 formed to have an approximately C-shaped cross-section for covering from a lower abdomen to buttocks and a seal member 14 provided on the peripheral part of the diaper cup 10 for sealing a gap between the diaper cup and a user. A lower abdomen covering part for covering the lower abdomen is made of a rigid member, and the seal member 14 is made of a hollow soft member having a cross section of an approximately ellipse, an oval, a trapezoid, or a rectangle. Parts from a lower abdomen contact part to one groin contact part, from one groin contact part to a buttocks contact part, from the buttocks contact part to the other groin contact part, and from the other groin contact part to the lower abdomen contact part are twisted, or the groin contact parts are thicker than the lower abdomen contact part so as to make the surface in contact with the user largest. Consequently, the automatic excretion disposal apparatus and the user-worn device which enable sufficient excretion and washing and are user friendly are provided.